The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Coupling devices are often used to couple the free ends of adjacent tubular ducts. Such devices are used extensively in aircraft applications, which typically have a large amount of ducting for routing various high pressure and/or high temperature fluids and/or airflows (e.g, engine bleed air, trim air, etc.). In commercial and military aircraft, such coupling devices can number 500 or more.
Present day coupling devices may suffer from various drawbacks, including “ballooning” at the gap area, which is typically between about 0.5 inch to about 4 inches in length, and which separates the free ends of two ducts. Ballooning may occur from a gradual weakening of the material from which the coupling device is constructed, in response to exposure to the high pressure fluid flowing within the duct, and to many hundreds or thousands of thermal cycles that the coupling device is exposed to. In particular, ballooning may occur from the repeated stretching and elongation of the elastomeric binder material of the device, which can also cause ruptures and leakage.
“Slippage” occurs when coupling device is not secured tightly enough to the ducts via the clamps. Occasionally the material of the coupling device that interfaces with and covers the free ends of the two ducts may itself be so incompressible that even when the clamps are tightened securely on the coupling device, the coupling device may still not be clamped tightly enough to the free ends of the duct. Over tightening of the clamps can also cause problems, and more particularly may cause the clamps to dig in to the material of the coupling device, thus weakening the material. Over tightening can also weaken the structure of the ducts themselves and/or damage the ducts.
Rupturing or tearing of the material of the coupling device may also occur over time. Tearing or rupturing may be caused by inherent weakness in the material used to form the coupling device, or possibly from fatigue caused by vibration, abrasion or periodic movement of the free ends of the ducts.
To address these issues, a metallic clamshell-like structure has often been employed to encapsulate the coupling device. The clamshell-like structure is arranged over the gap area between the free ends of the ducts and secured via clamps, for example hose clamps, or by other mechanical fastening systems including threadable bolts. As will be appreciated, this adds significant expense and complexity, not to mention a significant amount of added weight. In aircraft applications, added weight is particularly undesirable as additional weight reduces the payload of the aircraft or its operating range on a given amount of fuel.